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Idle air controller

Tiny
LANCE43
  • MEMBER
  • 1992 FORD CROWN VICTORIA
  • V8
  • 2WD
  • AUTOMATIC
  • 109,000 MILES
My car was stalling at idle, in gear and in park. I have changed spark plugs and wires. It ran fine while driving the car. I replaced the IAC and now it idles for a bit then I hear a loud humming noise the the idle rpm's go way up. While driving the car and the humming starts the car seems to want to accelerate. I have to use more brake to stop. When it gets to below twenty or thirty mph then the humming quits and the car stops easier.
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Wednesday, September 15th, 2010 AT 4:36 PM

16 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Hi lance43, Welcome to 2CarPros. Com.

Do you have a check engine light?

Clean the mass airflow sensor with an electronic cleaner CRC, and also test the throttle position sensor, closed idle and wide open throttle voltages. Let me know.
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Wednesday, September 15th, 2010 AT 5:13 PM
Tiny
LANCE43
  • MEMBER
  • 14 POSTS
I cleaned the MAF with CRC Mass Air Flow Cleaner.

I checked voltages with key on. I am attaching the pictures. No I do not have a check engine light.


https://www.2carpros.com/forum/automotive_pictures/416038_TPS_Wide_Open_2_1.jpg



https://www.2carpros.com/forum/automotive_pictures/416038_TPS_Closed_2_1.jpg

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Wednesday, September 15th, 2010 AT 6:37 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
You have a problem with the TPS it should not have that voltage 4.98 volts. It should be below one volt at closed throttle position and gradually increase as you smoothly rotate the throttle to that voltage 4.98 volts.
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Wednesday, September 15th, 2010 AT 6:44 PM
Tiny
LANCE43
  • MEMBER
  • 14 POSTS
I know that the TPS should also have.8 to 1.0 Ohms and I only get.003 Ohms. I have the meter set to 2M for resitance is this correct setting for the multimeter?

Also, are the probes in the correct position on the TPS plug? I have the black on ground and the red on VOL REF. But why would this happen when all I did was change the IAC valve?
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Wednesday, September 15th, 2010 AT 6:58 PM
Tiny
WAY2OLD
  • MECHANIC
  • 195 POSTS
The reference wire is a five volt wire. You are reading the correct voltage. Move the red lead to the signal return wire and the black to a good engine ground and see it the voltages fall in range. Look at the IAC to be sure the gasket is not the fault and leaking air by it to the engine.
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Wednesday, September 15th, 2010 AT 7:18 PM
Tiny
LANCE43
  • MEMBER
  • 14 POSTS
I checked the voltage with the red probe on the TPS signal wire and black to ground. Moving the throttle the voltage went from.96 volts to 4.70 volts.

I put gasket sealer on the valve before installing it. I cannot tell if its leaking or not with the engine noise.

I have been told that if the IAC is humming that means it is bad, is this true?
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Wednesday, September 15th, 2010 AT 7:37 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
The TPS is good, unplug the IACV if it quiets down, replace it.
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Wednesday, September 15th, 2010 AT 7:47 PM
Tiny
LANCE43
  • MEMBER
  • 14 POSTS
I unplugged the IAC and it does not hum anymore but it runs rough I had a hard time starting it. It would run rough then shut off. I hear a loud hissing from around the throttle body. I noticed on the air intake that the seal that attaches to the front of the TB is broke and is not making a good seal. So I removed it and it idled okay with the IAC unplugged. But I still hear the loud hissing, is this just the air being sucked into the throttle body?
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Wednesday, September 15th, 2010 AT 8:38 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Could just be the air rushing into the throttle body. Did you clean out the IACV valve passages before you replace?
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Thursday, September 16th, 2010 AT 1:02 AM
Tiny
LANCE43
  • MEMBER
  • 14 POSTS
No I did not clean them. What kind of cleaner would work, carburetor cleaner, MAF Cleaner?
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Thursday, September 16th, 2010 AT 9:09 AM
Tiny
LANCE43
  • MEMBER
  • 14 POSTS
Okay, I cleaned the passages with carburetor cleaner and reinstalled IAC still same problem. Running rough the high idle and humming.

Now I did notice that the large vacuum line coming from under the IAC has a lot of suction. When I plug it up car seems to run somewhat normal and the noise goes away. After a few seconds the suction stops and I unplug it and runs okay. If I touch the throttle then it goes right back to humming.
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Thursday, September 16th, 2010 AT 12:03 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Now I did notice that the large vacuum line coming from under the IAC has a lot of suction. Is this vacuum hose leaking?

Unplug the valve if it is operating properly the engine will shut off. If there are vacuum leaks it will stay running and you can listen, find and fix them. A lot of the time if the idle seems high when you start, hit it with a hammer, if the idle drops the valve is sticking, probably has a cracked piston in the valve and needs to be replaced.
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Thursday, September 16th, 2010 AT 4:59 PM
Tiny
WAY2OLD
  • MECHANIC
  • 195 POSTS
Replace that hose. Ford should still have them. Those are commonly known as a "Hooter Tube".
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Thursday, September 16th, 2010 AT 6:58 PM
Tiny
LANCE43
  • MEMBER
  • 14 POSTS
Okay, I will try rasmataz's idea to see of that works.

If I still have a problem I will try way2old's idea.

Thank you guys so much for your help.
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Thursday, September 16th, 2010 AT 7:26 PM
Tiny
KHARPER2
  • MEMBER
  • 1 POST
I have a 1997 Crown Victoria. The idle air control valve, spark plugs and fuel pump, mass airflow sensor, new radiator and top hose has been replaced. When sitting at a stop sign the car will shut off and check engine light comes on but the car cranks back up fine. What could be the issue?
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+1
Sunday, June 17th, 2018 AT 8:41 AM
Tiny
STEVE W.
  • MECHANIC
  • 13,414 POSTS
KHARPER2 Please, use this link to ask your question as a new one. Give as much information as you can.

https://www.2carpros.com/questions/new
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Monday, June 18th, 2018 AT 10:45 PM

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